Controlling MIMO layers for UE power saving

Abstract

This disclosure relates to techniques for dynamically adjusting a number of active receiver chains of a wireless device. Based on communication parameters exchanged with a base station, a device may determine a maximum number of receiver chains needed for data reception during one or more time periods. Such dynamic adjustment may enable power savings.

What is claimed is: 
     
       1. A method, comprising:
 at a base station:
 establishing a wireless communication link with a user equipment device (UE); 
 receiving, from the UE, a preference for a maximum number of multiple-input multiple-output (MIMO) layers for power savings at the UE; 
 configuring a first Bandwidth Part (BWP), wherein a configuration of the first BWP includes a first maximum number of MIMO layers specific to the first BWP; 
 configuring a second BWP, wherein a configuration of the second BWP includes a second maximum number of MIMO layers specific to the second BWP, wherein the second maximum number of MIMO layers is less than the first maximum number of MIMO layers; 
 transmitting, to the UE, data using the first BWP and using a first number of MIMO layers less than or equal to the first maximum number of MIMO layers; 
 transmitting, to the UE, an indication to switch to the second BWP configured with the second maximum number of MIMO layers to enable the power savings at the UE; 
 transmitting, to the UE, downlink control information, wherein the downlink control information indicates an actual number of MIMO layers less than or equal to the second maximum number of MIMO layers; and 
 transmitting data to the UE using the actual number of MIMO layers. 
 
 
     
     
       2. The method of  claim 1 , wherein the first bandwidth part is a default bandwidth part, wherein the first maximum number of MIMO layers is equal to one. 
     
     
       3. The method of  claim 1 , the method further comprising transmitting a second communication parameter to the UE, wherein the second communication parameter comprises a maximum number of layers to receive during a connected mode discontinuous reception (CDRX) on duration. 
     
     
       4. The method of  claim 1 , wherein the second maximum number of MIMO layers is less than or equal to the maximum number of layers for power savings at the UE. 
     
     
       5. The method of  claim 1 , the method further comprising transmitting a second communication parameter to the UE, wherein the second communication parameter comprises a media access control (MAC) control element (CE), wherein said transmitting the indication to switch to the second BWP is based at least in part on channel conditions. 
     
     
       6. The method of  claim 5 , wherein the MAC CE is transmitted to the UE during a first slot, wherein the second maximum number of MIMO layers is applicable to one or more second slots after the first slot,
 the method further comprising:
 determining a third maximum number of MIMO layers for communication with the UE, wherein the third maximum number of MIMO layers is determined based at least in part on a change in channel conditions; 
 transmitting a third communication parameter to the UE, wherein the third communication parameter indicates the third maximum number of MIMO layers, wherein the third maximum number of MIMO layers is applicable to one or more third slots after the one or more second slots; 
 transmitting, to the UE, second downlink control information indicating a second actual number of MIMO layers less than or equal to the third maximum number of MIMO layers; and 
 transmitting data to the UE using the second actual number of MIMO layers during the one or more third slots. 
 
 
     
     
       7. An apparatus, comprising:
 a processor configured to cause a user equipment device (UE) to:
 establish communication with a base station; 
 transmit, to the base station, a preference for a maximum number of multiple-input multiple-output (MIMO) layers for power savings at the UE; 
 receive, from the base station, a first communication parameter; 
 determine a maximum number of MIMO layers for a first bandwidth part, BWP, based on the first communication parameter; 
 receive, from the base station, a second communication parameter; 
 determine a second maximum number of MIMO layers for a second BWP based on the second communication parameter; 
 receive, from the base station, an indication to switch to the second BWP configured with the second maximum number of MIMO layers, wherein the switch to the second BWP configured with the second maximum number of MIMO layers enables the power savings at the UE; 
 receive, from the base station, downlink control information (DCI) indicating an actual number of MIMO layers equal to or less than the second maximum number of MIMO layers; and 
 receive, from the base station, downlink data using the actual number of MIMO layers. 
 
 
     
     
       8. The apparatus of  claim 7 , wherein the second maximum number of MIMO layers is less than or equal to the maximum number of layers for power savings at the UE. 
     
     
       9. The apparatus of  claim 7 , wherein the processor is further configured to cause the UE to:
 indicate to the base station a number of codewords supported by the UE, wherein the first maximum number of MIMO layers is associated with the number of codewords. 
 
     
     
       10. The apparatus of  claim 9 , wherein the maximum number of MIMO layers for power savings at the UE is based on one or more measurements of channel conditions. 
     
     
       11. The apparatus of  claim 7 , wherein the processor is further configured to cause the UE to:
 determine a dynamic maximum number of MIMO layers. 
 
     
     
       12. The apparatus of  claim 11 ,
 wherein the dynamic maximum number of MIMO layers is further based on at least one inactivity timer, wherein the at least one inactivity timer includes a BWP inactivity timer. 
 
     
     
       13. The apparatus of  claim 12 , wherein the at least one inactivity timer further includes a discontinuous reception (DRX) inactivity timer, wherein at least one of the first communication parameter and/or the second communication parameter includes a maximum number of layers for a connected mode discontinuous reception (CDRX) on duration. 
     
     
       14. The apparatus of  claim 11 , wherein the processor is further configured to cause the UE to:
 receive a further communication parameter from the base station, wherein the further communication parameter is received via a media access control (MAC) control element (CE); and 
 adjust the dynamic maximum number of MIMO layers based on the further communication parameter, wherein the processor is further configured to cause the UE to:
 depower at least one receiver chain plurality of receiver chains based on the adjustment to the dynamic maximum number of MIMO layers. 
 
 
     
     
       15. A user equipment device (UE), comprising:
 a radio; and 
 a processor operably connected to the radio and configured to cause the UE to:
 establish communication with a base station; 
 transmit, to the base station, a preference for a maximum number of multiple-input multiple-output (MIMO) layers for power savings at the UE; 
 receive, from the base station, a first communication parameter; 
 determine a maximum number of MIMO layers for a first bandwidth part, BWP, based on the first communication parameter; 
 receive, from the base station, a second communication parameter; 
 determine a second maximum number of MIMO layers for a second BWP based on the second communication parameter; 
 receive, from the base station, an indication to switch to the second BWP configured with the second maximum number of MIMO layers, wherein the switch to the second BWP configured with the second maximum number of MIMO layers enables the power savings at the UE; 
 receive, from the base station, downlink control information (DCI) indicating an actual number of MIMO layers equal to or less than the second maximum number of MIMO layers; and 
 receive, from the base station, downlink data using the actual number of MIMO layers. 
 
 
     
     
       16. The UE of  claim 15 , wherein the DCI is received from the base station during a first slot, wherein the processor is further configured to cause the UE to:
 depower at least one active receiver chain during the first slot, wherein the downlink data is received during the first slot and subsequent to said depowering; and 
 repower the at least one active receiver chain for at least a portion of a subsequent slot. 
 
     
     
       17. The UE of  claim 15 , wherein the maximum number of layers for power savings at the UE is greater than or equal to the second maximum number of MIMO layers. 
     
     
       18. The UE of  claim 17 , wherein the second maximum number of MIMO layers is equal to the maximum number of MIMO layers for power savings at the UE. 
     
     
       19. The UE of  claim 15 , wherein the processor is further configured to cause the UE to:
 determine a dynamic maximum number of MIMO layers. 
 
     
     
       20. The UE of  claim 19 ,
 wherein the dynamic maximum number of MIMO layers is further based on at least one inactivity timer, wherein the at least one inactivity timer includes a BWP inactivity timer.